Nomograph for Thermometer Temperature Correction P. J. COLE, Barrett Division, Allied Chemical & Dye Corporation, Philadelphia, Pa. where c = final temperature correction, " C. (emergent stem and pressure); C = emergent stem correction only; N = length of emergent mercury stem measured, " C.; T = temperature being corrected; t = average temperature of emergent mercury stem; P = barometer reading, mm. of mercury; and d t / d p = variation in boiling point per mm. of pressure change for particular compound being distilled. This factor can be determined experimentally or calculated from the Clausius-Clapeyron equation. The nomograph is used as follows:
pu' MOST distillation work, particularly in fractional distilla-
I tion, temperature readings must correspond to total immersion
of the thermometer mercury and to a fixed pressure, usually 760 mm. of mercury. IVhen partial immersion thermometers are used, it is necessary only to correct the reading to 760 mm. For accurate work, however, thermometers graduated in 0.2" C. or less are used, and such thermometers are usually of the total immersion type. In this case it is necessary to correct both for emergent mercury stem and for pressure. In fractional distillation work where temperature readings are taken a t frequent intervals, the calculation of the correction is time-consuming and tedious. The time required is greatly reduced, and all calculations are eliminated by the use of a nomograph. The nomograph shown here is based on the regular formulas for emergent stem correction for mercury-in-glass thermometers,
Determine T - t and connect this point on A by means of a straightedge to the emergent stem in C. on N . Determine the point of intersection on C and connect this point with the barometric pressure in millimeters on D. The intersection on the d t / d p line for the vapor under consideration gives the final correction for T for total immersion and 760-mm. pressure. Example. Assume in a fractional distillation a t atmospheric pressure that the vapor under consideration is substantially phenol. The temperature of the vapor is T = 179.8"; the average temperature of the emergent stem (determined by means of a thermometer placed near the mid-point of the emergent mercury stem) is observed to be 30" C., and the emergent mercury stem has a length of 40" C. The barometer is 750 mm. For phenol
- t ) 0.000156
C = N(T
and for reducing boiling points to sea level, c =C
-
A
(P
- 760)---a t
C
4.8
-
FINAL TEMPIRATIJRK COPPEC1ION 'C.
720
i
4.6 -4.4
--
4.2
--
260
4.0
--
2 SO
3.8 --
240
3.6 --
730
3 4 --
3.2 -3.0
D
--
1.8 -2.6
--
2.4 -2.2 --
-1.8 --
2.0
I. 6 -1.4
--
1.2 --
-0 - 8 -1.0
0.6
a4
--
-+
EMERGENT
BAROMc TRIC
STEMCORRECTION
?RE5 5 U RE
946
V O L U M E 2 2 , NO. 7, J U L Y 1 9 5 0 Table I. Benzene Tnliiene
XYli&i Ethylbenzene Pseudocumene Mesitylene Styrene Phenol Cresols Pyridine Quinoline haphthalene Cyclohexane
Values of d t l d p for Various Compounds 0.043 0.046 0.049 0.049 0.052
0.051 0.049 0.045 0.050
0.047
0.058
n-Heptane n-Octane n-Decane Tetralin Aniline o-Toluidine Dimethylaniline Carbon tetrachloride Ethylene dichloride Chloroform Acetic acid
0.058 0.044
d t l d p = 0.045. Then T - t = 149.8. Connect 150 on A with 40 on ,V by means of a straightedge; the reading on C is 0.95. This is the emergent stem correction. Connect this point with 750 on D. The intersection on the d t l d p = 0.045 line gives the final
947 correction of 1.4' C., or a corrected temperature of 179.8 181.2' c.
+ 1.4 =
The nomograph is designed for correcting the temperature readings of total immersion thermometers used in distillations carried out a t atmospheric pressure. For distillations a t reduced pressures the use of d t l d p to correct to 760 mm. does not apply. In this case lines A and N are used to obtain the emergent stem correction on C only. I t is then necessary to correct to 760 mm. by means of the integrated form of the Clausius-Clapeyron equation or experimentally determined vapor-pressure curves, If partial immersion thermometers are used instead of total immersion, it is only necessary to correct for pressure. I n this case the straightedge is used to connect the 0 of line C with the barometric pressure on D. The intersection with the proper d t / d p line gives the temperature correction for pressure. RECEIVED .4pril 8, 1948.
Determination of Sulfur Dioxide in Presence of Sulfur Trioxide SYDR'EY ATKIK, Chemical Construction Corporation, Linden, N . J .
N ACCURATE colorimetric method has been developed for
A determining small quantities of sulfur dioxide in gases re-
sulting from the catalytic manufacture of sulfuric acid. The colored solution formed by combining sulfur dioxide with fuchsinformaldehyde reagent in an acid medium follows Beer's law up to a concentration of 1 mg. of sulfur dioxide in 500 ml. of solution at 2 5 O += 3" C. The composition of converter exit gases encountered in sulfuric acid manufacture is of interest in studying catalytic efficiency. The sulfur dioxide content of such gases is determined by a combination of methods suggested by Haller (3) and Grant (2). Haller absorbed the sulfur dioxide and the sulfur trioxide from a gas completely with a relatively simple apparatus in 10% sodium hydroxide solution containing 5% glycerol, which effectively prevented oxidation of the sulfur dioxide. Steigman (6) used fuchsin and sulfurous acid to determine the concentration of formaldehyde by measuring the intensity of the color produced. The method was employed with complete success in determining the sulfur dioxide of the convei-ter exit gas in a contact sulfuric acid plant. A gas containing 8% trioxide was effectively analyzed. It was found that sulfur dioxide in concentrations up to 1 mg. in the scrubbing solution diluted to 500 ml. at room temperature followed Beer's law. The method is adaptable for long or short tests. Results showing the average composition of the gas over fairly long periods are obtained by diluting the absorption liquor and taking an aliquot containing less than 1 mg. of sulfur dioxide. The methods described in the literature for the determination of small quantities of sulfur dioxide in an excess of air with a comparatively high concentration of sulfur trioxide are involved and subject to error. Work was carried out with the primary object of finding a reliable method for the determination of sulfur dioxide in the gases resulting from the catalytic production of sulfuric acid. The Reich test by Dragt and Greenan ( 1 ) was investigated thoroughly. This method is suitable for analyzing the gases entering the converter and leaving the stack. I t is a very handy and rapid method for control work in commercial processes, but it is dependable only for a gas Containing a negligible sulfur trioxide content; for reasons unknown, to the author high results are obtained when sulfur dioxide is determined in a sulfur trioxide gas. If analysis of the converter exit gas is required for investigation purposes, the method below may prove to be valuable. .4n attempt was made to eliminate the sulfur trioxide before testing for sulfur dioxide by scrubbing the gas with concentrated
sulfuric acid. The sulfuric acid scrubbers were good for only a very limited period while running the Reich test. As the acid strength increased, there was a tendency to strip dissolved sulfur dioxide from the acid, giving high results.
A
i
l
Figure 1.
Absorption Apparatus
A.
Calcium chloride tube B. End of test tube, 0.75 inch i n diameter and 1 inch high C. Thermometer D. 250-1111. buret E. Leveling bottle F . Pinchclamps
The Reich test has an uncertain end point, owing to the large excess of iodine mixed with the starch solution, and gives the sulfur dioxide content of the gas only a t the moment the test is made. Reis and Clark ( 4 ) absorbed the sulfur dioxide and sulfur trioxide in a gas in a sodium hydroxide solution containing stannous chloride and then titrated the strongly acidified solution with 1 A'
